Wholly aromatic polyester resins have long been known. For instance, 4-hydroxybenzoic acid homopolymer and copolymers have been provided in the past and are commercially available. Such polymers are commonly crystalline in nature, relatively high-melting or possess a decomposition temperature which is below the melting point, and when molten frequently exhibit orientation in the melt.
The homopolymer of p-hydroxybenzoic acid is a very high-melting, insoluble material and, hence, very difficult to fabricate. Melting points as high as 610.degree. C. were quoted--see W. J. Jackson, The British Polymer Journal, December 1980, p. 155. In order to depress the high melting point of the homopolymer so as to make it melt-fabricable, a variety of materials incorporating different types of comonomers were prepared over the years.
One such material is, for example, the resin made from p-hydroxybenzoic acid (PHBA), isophthalic (IA) and/or terephthalic acids (TA), and 4,4'-biphenol (BP) as described in, for example, Cottis et al., U.S. Pat. Nos. 3,637,595 and 3,975,487. The polymer has outstanding high-temperature properties; it can be molded to give articles of high modulus and strength. It is offered commercially by Amoco Performance Products, Inc. under the tradename of XYDAR.RTM. Due to the use of PHBA and BP, these polymers can be expensive.
A related class of wholly aromatic polyesters based on p-hydroxybenzoic acid, isophthalic and terephthalic acids, and hydroquinone (HQ) is claimed in commonly assigned U.S. patent application entitled "Hydroquinone Poly (Iso-Terephthalates) Containing Residues of p-Hydroxybenzoic Acid," Ser. No. 07/255,670, filed in the names of R. Layton et al., on Oct. 11, 1988, which is hereby incorporated by reference. The polymers described in the latter application display high modulus and high strength; they have melting points in the range of from 340.degree. C. to 400.degree. C., are melt-processible, and show orientation in the molten state. Compositions filled with about 30 weight percent of glass fibers display heat distortion temperatures (HDT's) of about 240.degree. C. to about 280.degree. C., when measured under a load of 264 psi.
While the overall combination of properties of the above resins is outstanding compared to prior art wholly aromatic polyesters based on p-hydroxybenzoic acid, benzene dicarboxylic acids and hydroquinone, they are preferably used in blends with polyesters made from p-hydroxybenzoic acid, isophthalic and terephthalic acids and 4,4'-biphenol to facilitate moldability and minimize blistering of large molded parts. In addition, these novel blends display improved mechanical properties; composites containing 30 weight percent of glass fibers show heat distortion temperatures (under a load of 264 psi) of at least 240.degree. C. The subject blends are claimed in commonly assigned U.S. patent application of P. Huspeni et al., entitled "Polymer Compositions Having Improved Molding Characteristics," Ser. No. 07/255,632, filed on Oct. 11, 1988. These cases are hereby incorporated by reference.
Also, we filed concurrently herewith two applications to heat resistant and high-strength polymers and blends of hydroquinone poly (Iso-Terephthalates) containing residues of p-hydroybenzoic acid by R. Layton et al. which are a continuation-in-part of U.S. Ser. Nos. 255,670 and 255,632 filed Oct. 11, 1988, our case Nos. 29723 and 29724. These polymers and blends have good mechanical properties, good fiber ratings and ability to vapor phase solder.
We considered that if it is possible to incorporate many or all of the desirable properties of a blend into a single polymer in order to avoid producing two different polyesters, it would be desirable.
We have now found that wholly aromatic polyesters based on five components, i.e., p-hydroxybenzoic acid, isophthalic and terephthalic acids, hydroquinone, and an arylene diol such as 4,4'-biphenol, for example, used in specified proportions, display excellent mechanical properties, good moldability, high melting points, high HDT's, good fiber ratings, and yield molded parts having very good surface characteristics.
The present discovery was surprising since with some known exceptions, blends of polymeric materials are generally different from polymers. They are immiscible, that is, they consist of domains of chemically distinct phases. Usually, one component forms a continuous phase, while the other component forms roughly spherical domains as inclusions. Under some circumstances, bi-continuous structures are also obtainable. Hence, a blend of two polymers is usually a two-phase system whose properties reflect those of both phases present. On the other hand, a random copolymer is a one-phase material wherein the properties of the constituents are averaged. Thus, a copolymer is expected to be quite different from a two-phase blend. Even if the monomers employed to make the component polymers of the blend were to be the same as those employed to make the corresponding random copolymer, one would not expect similar characteristics for the two systems. In addition, the known prior art suggests that one would not be able to find any useful materials in the compositional region of the instant invention. In fact, the prior art teaches away from the compositional ranges of the current invention.
As indicated in application Ser. No. 07/255,670 filed Oct. 11, 1988 by R., Layton et al. and assigned to Amoco Inc., the prior art has been unsuccessful in replacing biphenol with hydroquinone without sacrificing properties and/or using expensive comonomers. While various references discussed below have suggested employing mixtures of hydroquinone and a second arylene diol, none of these describe the polymers of this invention.
Dicke et al., U.S. Pat. No. 4,603,190, claim five component copolyesters based on terephthalic acid, isophthalic acid, p-hydroxybenzoic acid, hydroquinone and 4,4'-biphenol wherein the terephthalic acid to isophthalic acid ratio is equal to or less than one. The polymers display Vicat B temperatures of about 130.degree. C. to about 150.degree. C., which translate into even lower HDT's. Polymers with such low Vicat B temperature would be of no interest in applications which require dimensional stability at high temperatures (e.g. equal to or greater than about 200.degree. C.).
Portugall et al., U.S. Pat. No. 4,751,128, claim five similar component polyesters wherein the molar ratios of terephthalic to isophthalic acids vary from 1.04:1 to 19:1; and wherein the hydroquinone to 4,4'-biphenol molar ratios are in the range of 0.1:1 to 2.67:1. The copolymers appear to have a satisfactory combination of mechanical and thermal properties with HDT's of up to 248.degree. C. The drawback of the materials, however, is their high cost due to the rather low ratio of the inexpensive hydroquinone to the very expensive 4,4'-biphenol. In fact, U.S. Pat. No. 4,751,128 suggests that there are no compositions of interest at hydroquinone to 4,4'-biphenol molar ratios greater than 2.67:1; indeed, according to the patent, it is preferred that the subject ratio be no higher than 2.33:1 (column 2, lines 24-26).
Okamoto et al., European Patent Application No. 275,324, disclose and claim aromatic polyesters from isophthalic and terephthalic acids, p-hydroxybenzoic acid, hydroquinone, 4,4'-biphenol, and, optionally, a sixth comonomer selected from 2,6-naphthalene diol, or an alkyl- or chloro- substituted hydroquinone. Once again, the mole ratio of hydroquinone to the 4,4'-biphenol is low, i.e. from 1:1 to 1:19. In fact, polymers outside of the molar percentage criteria are considered undesireable. The application discloses (p. 6) that if the mole percentage of biphenol is less than 50 mole percent (i.e., the HQ/BP ratio is greater than 1:1), "the heat resistance is poor" (line 9, p. 6); while if the mole percentage of biphenol is more than 0.95 mole percent (i.e., the HQ/BP ratio is lower than 1:19), the resulting polymers have poor flow characteristics (See also p. 6). It is noteworthy, that copolymers with hydroquinone/4,4'-biphenol molar ratios greater than one could not be prepared since they solidified during polymerization (see lines 12-17, p. 14; and Table 2, p. 15).
Analysis of the foregoing patents (i.e. U.S. Pat. Nos. 4,603,190 and 4,751,128; and European Patent Application No. 275,324) also indicates that the polyesters described therein comprise high amounts of another expensive monomer, namely, p-hydroxybenzoic acid (PHBA). Contrary to the commonly held belief that good high-temperature properties of wholly aromatic polyesters can be achieved only at high contents of p-oxybenzoyl moieties, it was now unexpectedly discovered that materials exhibiting excellent high temperature performance can be obtained at very low PHBA contents; even at terephthalic acid to isophthalic acid ratios of less than one.
Cottis et al., U.S. Pat. No. 4,563,508, suggest the possibility of preparing copolyesters from terephthalic and isophthalic acids, p-hydroxybenzoic acid, hydroquinone and 4,4'-biphenol. Cottis, U.S. Pat. No. 4,563,508, is directed to the improvement of molding compounds based on wholly aromatic polyesters by the addition of a minor amount of a flow modifier. The flow modifier crystallizes poorly and improves the flow of the highly crystallized base polymer it is added to. The flow modifier does not enhance the end properties of the blend composition. It is to be noted that the addition of the flow modifier decreases the HDT of the composition and does not increase the strength. The patent does not describe any compositions within the scope of this invention.
In summary, therefore, the possibility of preparing polyesters from terephthalic acid, isophthalic acid, p-hydroxybenzoic acid, hydroquinone and an arylene diol such as 4,4'-biphenol, for example; with high molar ratios of hydroquinone/arylene diol [e.g. .gtoreq.3:1 and at low PHBA contents, e.g., about 0.4 to 0.6 (vide infra)]; having both the desirable thermal, mechanical and molding characteristics as hereinbelow described; and very attractive economics was surprising and totally unexpected. In fact, the teachings of the prior art are contrary to our discoveries.